OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What happens to oxygen during gas exchange in the lungs?

It diffuses into the alveolus
It is stored in alveoli
It diffuses into the blood
It is expelled and breathed out

The correct answer is: It diffuses into the blood

During gas exchange in the lungs, oxygen diffuses into the blood from the alveoli. This process occurs due to the difference in concentration, where the concentration of oxygen is higher in the alveoli (the tiny air sacs) compared to that in the deoxygenated blood arriving in the capillaries surrounding the alveoli. As a result of this gradient, oxygen molecules move from the area of higher concentration in the alveoli into the blood, where it binds to hemoglobin in red blood cells for transport throughout the body. Understanding this process is crucial because it highlights the primary function of the lungs in facilitating the delivery of oxygen to the bloodstream and subsequently to tissues, enabling cellular respiration and energy production.